In order to reduce wear on the scraping edge of scraper rings employed as interior seals for rotary piston engines, it has been proposed to apply to the external face of the ring, including the scraping edge, a chromium layer. Alternatively, the radially innermost bounding surface of the ring, at least in the zone nearest the associated part of the housing has been provided with a hard abrasion-resistant layer, preferably of chromium.
It has been found that there is always the problem of retention of this wear-resistant layer on the base material because it may not withstand the loads applied, so that it may subsequently crumble off. Besides, chrome cladding processes that are normally employed are costly, particularly as a pore-free chromium texture is required.